1. Field of Invention
The present invention relates to class B amplifiers and more specifically to a class B amplifier with a process variation independent deadband.
2. Description of Related Art
A class B amplifier with a differential input produces a deadband at its output that is a result of the input signal at zero volts. The deadband produces a distortion at the output, and control of the deadband to eliminate the distortion effect has been semiconductor process dependent, which causes a widening of the deadband to allow for process variations. This allowance for process variations makes the deadband be wider than it could otherwise be and can extend over a wide range of the input signal causing a substantial distortion in the output signal.
Class B amplifiers are useful for low power applications, where the input signal is a differential signal and the output is used to control a device such as a motor. In this case a wide deadband prevents optimum control of the motor in and around the crossover between a positive and negative input signal. Reducing the width of the deadband is critical to good motor control in and around a zero input signal of a class B amplifier.
In U.S. Pat. No. 6,710,660 (Shacter) a deadband amplifier design is directed to a class B power amplifier with rail-to-rail output swing and a small deadband. U.S. Pat. No. 4,588,960 (Salama et al.) is directed to a class B amplifier used for low voltage and low power integrated circuit applications. U.S. Pat. No. 3,821,625 (Scholl) is directed to an amplifier design where a second stage has a high gain and output signal to compensate for a deadband in the output signal. U.S. Pat. No. 3,699,464 (Zobel) is directed to an amplifier with a deadband in which the common mode range is widened, allowing the deadband to be adjusted by adjusting current sources coupled to the output stage.
A need exists to create a class B amplifier for use in integrated circuits that has a well-defined narrow deadband that is independent of semiconductor process variations, and providing a positive voltage for a non-zero input signal. This would provide an improved control of subsequent stages for input signals in and around the crossover between a negative and positive input signal.